所以我写了下面的测试，以找出是否我有个好主意与否，似乎是m的做法是正确的。在的onCreate 我们修改的WeakReference 和投递的邮件将始终被传递到在前台活动。如果更改此code总是创建的onCreate 一个新的处理程序，你会发现更新消息没有得到传递。

So I wrote the following test to figure out whether I had the right idea or not and it seems that m approach is correct. In onCreate we change the WeakReference and the posted message will always get delivered to the activity that is in the foreground. If you change this code to always create a new Handler in onCreate you'll notice the update messages do not get delivered.

public class MainActivity extends Activity {

    private static int COUNT = 0;

    static LoginHandler mHandler;

    private static class LoginHandler extends Handler {

        private WeakReference<MainActivity> mTarget;

        LoginHandler(MainActivity target) {
            mTarget = new WeakReference<MainActivity>(target);
        }

        public void setTarget(MainActivity target) {
            mTarget.clear();
            mTarget = new WeakReference<MainActivity>(target);
        }

        @Override
        public void handleMessage(Message msg) {
            // int duration = Toast.LENGTH_LONG;
            // process incoming messages here
            MainActivity activity = mTarget.get();
            activity.update(msg.arg1);
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        if(mHandler == null)
            mHandler = new LoginHandler(this);
        else
            mHandler.setTarget(this);

        ((Button)findViewById(R.id.button)).setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                Message msg = new Message();
                msg.arg1 = COUNT++;
                mHandler.sendMessageDelayed(msg, 3000);

            }
        });

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    private void update(int count) {
        ((TextView) findViewById(R.id.hello_world)).setText("Hello World @ "+ count);
    }

}